This invention relates to a process for enhancing the activity of a promoted copper catalyst useful for selectively hydrogenating alpha-acetylenes in the presence of olefins in a liquid hydrocarbon stream.
Product streams of normally liquid or liquefiable olefins and diolefins such as propylene, butenes, pentenes, butadiene, and isoprene in particular are usually contaminated with small amounts of acetylenic impurities which are undesirable and often have to be removed at least to the level of a few parts per million in order for the stream to meet process requirements, for example, in polymerization processes or to avoid formation of explosive metal acetylides in equipment. These acetylenic impurities are essentially the alpha-acetylenes corresponding to the olefins and diolefins present as listed above.
It is known that acetylenic impurities can be selectively hydrogenated and thereby removed from a gas stream by passing a mixture of the gas with hydrogen over a copper catalyst of moderate activity. Such a method is described in our U.S. Pat. Nos. 3,076,858 and 3,327,013. More recently, a highly activated copper catalyst has been found to be very effective for removing acetylenic contaminants from a hydrocarbon stream by catalyzing the selective reduction of alpha-acetylenes with hydrogen dissolved in the liquid hydrocarbon stream. This process is described in our U.S. Pat. No. 3,912,789.
Previously known methods for regenerating this catalyst after its activity has declined substantially upon prolonged use have been based on repeated reduction by hydrogen. Although such regeneration is effective in many cases, when the loss of catalyst activity is caused by the cumulative effect of sulfur compounds present in the stream being treated, hydrogen reduction is relatively ineffective. Sulfur compounds commonly encountered include H.sub.2 S, lower alkyl mercaptans, organic sulfides and disulfides, COS, SO.sub.2, and SO.sub.3. Furthermore, when the stream is contaminated by more than the merest traces of sulfur, poisoning of the catalyst and consequent loss of activity proceed rapidly and the life of the catalyst becomes impractically short.